1. Field of the Invention
This present invention relates generally to the field of binding pages together in book form, and more particularly, to adhesive binding means and methods utilizing substrate strips backed with various heat-activated adhesives.
2. Background Art
It is often desirable to bind pages in book form. While clips and staples are often used to bind pages, pages bound by these means are frequently inadvertently pulled out and lost. Books bound by means of adhesives can be made to resist separation of pages and are thus more durable.
Furthermore, pages bound by means of adhesives can be more precisely constrained relative to each other. For this reason the pages of an adhesive bound book can be kept in flush alignment. This makes pages bound by means of adhesives more aesthetically attractive and easier to use.
The adhesives holding the pages of a bound book are preferably covered by heavy substrate of formable material. One reason is that printing can be placed on this substrate, and this printing will be visible when the book is viewed edge-wise. Another reason for using a substrate covering is that the outer substrate surface insulates the adhesive and the bound edges of the pages, which prevents wear on the binding. Another reason for using a substrate covering is that such substrates are considered more aesthetically appealing than exposed adhesive. Yet another reason for using a substrate covering is that the substrate is a convenient vehicle for applying adhesive to the pages during the binding process.
In response to this demand for heat-activated adhesive book bindings, several types of adhesive strips have been developed to bind pages. The principle behind these adhesive binding strips is that a piece of formable substrate material carries adhesive on one of its surfaces. The strip is placed across the edge of a stack of pages to be bound, heated to activation temperature, and then cooled so that the adhesive bonds all pages in the stack configuration. The adhesive remains substantially between the bound edges of the pages and the substrate strip.
U.S. Pat. No. 3,531,358 to Rost et al., discloses an adhesive strip which is wrapped partially around the first and last pages, herein sometimes referred to as the cover pages, of the book to form a larger bond area with the cover pages. This provides a more durable bond between the adhesive strip and cover pages.
One shortcoming present in some adhesive binding strips is that the adhesives which provide optimum bonding characteristics exhibit a low viscosity plastic state during the binding process, and as a result, the adhesive runs out from under the sides of the substrate strip onto the cover pages. Adhesive may also run out at the ends of a book binding.
U.S. Pat. No. 4,496,617 to Parker, which is hereby incorporated by reference, discloses a dual adhesive binding strip which overcomes part of the previously-described shortcoming of adhesive run out. The dual adhesive binding strip there disclosed employs a relatively thick (i.e. dimensionally thick in the direction normal to the surface of the substrate), high viscosity adhesive band on either side of a low viscosity adhesive band. These adhesive bands run in the direction of the desired binding (hereinafter called the "longitudinal" direction). The low viscosity adhesive band provides optimum bonding to the pages of the book. The relatively thick high viscosity adhesive bands are sufficient to bond the cover pages, while being of sufficient thickness to keep the low viscosity adhesive from running out of the longitudinal sides of the substrate strip.
Heat-activated strips according to this configuration may be bound by a machine disclosed in U.S. Pat. No. 5,052,873 to Parker. The machine there disclosed moves a binding strip into position abutting a stack of pages. The machine applies heat and pressure, sufficient to activate the adhesives, to the portion of the strip over the front cover, the portion of the strip over the page edges, and the portion of the strip over the back cover. When the adhesive cool, a finished binding results.
However, the potential problem of adhesive run out at the ends of the book binding remains. Adhesive run out at the ends of the substrate strip is aesthetically unattractive to the extent that exposed adhesive sets and hangs off of the ends of the book binding. Adhesive run out at the ends of the substrate strip is also a problem to the extent that the adhesive run out falls away from the book. This kind of adhesive run out is troublesome especially when it contaminates the workings of a binding machine, thereby causing binding machine failure.
One attempted accommodation is disclosed in U.S. Pat. No. 3,847,718 to Watson. This patent discloses a relatively thick band of low viscosity adhesive surrounded by a much thinner area of high viscosity adhesive. However, the potential for run out of the low viscosity adhesive remains because relatively thick low viscosity adhesive band can spill over the thin layer of high viscosity adhesive.
When the adhesive band is set back sufficiently away from the ends of the substrate to prevent run out, however, a thickness discontinuity can be observed in the finished bindings at the ends of the binding in the area where the low viscosity ends and the high viscosity adhesive begins.
Furthermore, the thin layer of high viscosity adhesive at the end of the binding does not adhere well to the edges of the bound pages, and as a result, a short fringe at each end of the substrate material remains unbound to the pages. While this unbound substrate material does not interfere with the creation of a strong bind, this free-hanging substrate gives the appearance of a poor bind. Also, small tears may develop in the free-hanging substrate, which exacerbates the appearance of a poor bind. Furthermore, there is a potential for increased wear on the corners of the pages at the ends of the binding.
The present invention overcomes the above-noted disadvantages of prior art devices. The disclosed adhesive binding strip provides for placement of high viscosity adhesive all around a low viscosity adhesive band. The low viscosity adhesive provides optimal bonding to the pages. The high viscosity adhesive can be placed on the substrate so that it will bind the entire substrate strip to the pages while preventing any run out of the low viscosity adhesive. These and other advantages of the subject invention will become apparent upon a reading of the following detailed description of the invention together with the appended claims and the drawings.